The present invention relates to a process for producing (+)-cis-homocaronic acid in surprisingly high yields from 2-caren-4-ol, 2-caren-4-one, 3-caren-2-ol, or mixtures thereof. The process consists of ozonizing the reactants to form the ozonides and then oxidizing the ozonides to yield (+)-cis-homocaronic acid. The (+)-cis-homocaronic acid is an important synthetic intermediate for producing (+)-trans-chrysanthemic acid. Natural and synthetic pyrethroid insecticides may then be made using the (+)-trans-chrysanthemic acid as an essential constituent.
One previously proposed procedure for synthesizing (+)-cis-homocaronic acid is described in U.S. Pat. No. 3,565,915 issued to Matsui, et al. However, the reactant 2-caren-4-one oxime, obtained from 3-carene, is used as the starting material. This oxime is oxidized with potassium permanganate to obtain the desired optically active (+)-cis-homocaronic acid. However, the Matsui patent notes that the production of (+)-cis-homocaronic acid by the oxime is hindered by the "exceedingly low yield".
One advantage of the present inventive process is that the yields obtained therefrom are much higher than from previously proposed processes. In fact, the theoretical yields from the present invention are in excess of 90%. The yields are high enough so that the process may economically be practiced on an industrial scale. Additionally, ozonization of the starting reactants involves a less expensive and more easily controlled method to produce the desired (+)-cis-homocaronic acid than use of potassium permanganate suggested in the Matsui patent above.